1. Field of the Invention
The present invention relates to a water-decomposable absorbent article for pantiliners, sanitary napkins, incontinence pads, disposable diapers and the like.
2. Description of the Related Art
Recently, absorbent articles disposable in flush toilets have come available, including, for example, pantiliners, sanitary napkins, incontinence pads, disposable diapers and the like.
Such water-decomposable absorbent articles comprise a combination of materials easily decomposable in water, in which the water-decomposable materials are bonded to each other. If the water-decomposable materials are not bonded firmly to each other in some degree in them, the water-decomposable absorbent articles could not retain their shape during their use, arid will be loosened to lose their fittability to the skin of wearers or will be broken. However, if the constituent water-decomposable materials are bonded too firmly to each other, they could be hardly peeled from each other in flush toilets and septic tanks.
If the water-decomposable materials constituting such absorbent articles could not be immediately separated into the individual constituent layers in septic tanks, the absorbent articles could hardly sink therein owing to the air existing in their layers. When the water-decomposable materials are sunk in septic tanks to receive a large amount of water therein, they can be readily decomposed in water and biodegraded in microorganisms living in water. Therefore, if absorbent articles could not sink in septic tanks, they will be decomposed extremely slowly.
To that effect, water-decomposable absorbent articles are required to have two contradictory functions, one being the bonding strength to ensure shape retention during their use and the other being the rapid decomposability in water after discarded. To meet this requirement, for example, International Unexamined Patent Publication (Kohyo) No. Heisei 11-500341 discloses an absorbent article comprising a water-decomposable top sheet, a water-decomposable back sheet and a water-decomposable absorbent layer sandwiched between the two sheets, in which the constituent components are bonded to each other with a water-soluble adhesive disposed therebetween.
The absorbent article disclosed in this publication is so constituted that no absorbent layer exists in the peripheral region, and the top sheet and the back sheet are bonded to each other with a water-soluble hot-melt adhesive or a water-soluble emulsion adhesive disposed therebetween in the peripheral region.
However, in the absorbent article disclosed in International Unexamined Patent Publication (Kohyo) No. Heisei 11-500341, a water-soluble hot-melt adhesive is applied to the peripheral region to form a spiral adhesive pattern therein, or a water-soluble emulsion adhesive is applied thereto. In this, therefore, the adhesiveness between the top sheet and the back sheet in the peripheral region of the absorbent article is not satisfactory. In that condition, the top sheet and the back sheet are often peeled off from each other in the peripheral region while the absorbent article is used, and, as a result, the absorbent article could not retain its shape, and will be often loosened or broken during its use.
An object of the present invention is to provide a water-decomposable absorbent article in which the constituent components are more firmly bonded to each other in the peripheral region of the article to thereby enhance the shape retention of the article during its use, but could be readily separated from each other when disposed of in flush toilets.
According to one aspect of the invention, a water-decomposable absorbent article may comprise a water-decomposable back layer, a water-decomposable and liquid-pervious surface layer, and a water-decomposable absorbent layer sandwiched between the back layer and the surface layer and having a smaller planar dimension than the back layer and the surface layer, wherein;
the absorbent article including an inner region in which the absorbent layer is present, and an outer peripheral region having the back layer and the surface layer bonded to each other without interposing the absorbent layer therebetween and being formed in a predetermined width spaced from a peripheral edge of the absorbent article; a thermoplastic water-soluble adhesive is applied in a strip shape between the back layer and the surface layer in a predetermined width along the peripheral edge in the outer peripheral region; and the back layer and the surface layer are heat-sealed with the thermoplastic water-soluble adhesive disposed therebetween in the outer peripheral region.
For example, the thermoplastic water-soluble adhesive is polyvinyl alcohol (PVA), more preferably a cold water-soluble polyvinyl alcohol derivative.
In the invention, the outer peripheral region of the absorbent article is heat-sealed with a thermoplastic water-soluble adhesive, for example, with PVA, disposed in a predetermined width of the outer peripheral region. Therefore, the shape retention of the absorbent article during its use is good. The bonding between the layers in the region ensures high adhesiveness in dry. During its use, the absorbent article mainly receives body fluid in an inner region, and the body fluid absorbed by it hardly spreads to the outer peripheral region. Therefore, the surface layer and the back layer are hardly peeled off from each other in the outer peripheral region, so that the shape of the absorbent article can be easily retained during its use.
When the absorbent article is, after used, disposed of in flush toilets, the water-soluble adhesive such as PVA, swells and dissociates in water, and the back layer and the surface layer are peeled off from each other. As a result, the constituent layers of the thus-disposed absorbent article are separated from each other and are readily decomposed in septic tanks, etc.
In particular, in the outer peripheral region of the absorbent article, no absorbent layer is sandwiched between the back layer and the surface layer, and the back layer and the surface layer are directly bonded to each other with the water-soluble adhesive disposed therebetween. Accordingly, the absorbent article is well self-retainable as a whole, and after it is disposed of, the back layer and the surface layer constituting it are readily peeled off from each other and all the constituent layers are therefore readily separated from each other.
Preferably, in the absorbent article of the invention, a layer of the thermoplastic water-soluble adhesive is formed almost entirely both in the outer peripheral region of the article and in the inner region thereof inside the outer peripheral region. For example, the thermoplastic water-soluble adhesive layer is made of an independent film disposed separately from the back layer. Preferably, the film for the thermoplastic water-soluble adhesive layer is laminated on the back layer.
In case where the thermoplastic water-soluble adhesive layer is disposed almost entirely on the back layer with the absorbent layer overlying the back layer in the preferred manner as above, the thermoplastic water-soluble adhesive layer can prevent liquid permeation through it and therefore can prevent body fluid from passing outside through the back layer.
According to another aspect of the invention, a water-decomposable absorbent article may comprise a water-decomposable back layer, a water-decomposable and liquid-pervious surface layer, and a water-decomposable absorbent layer sandwiched between the back layer and the surface layer and having a smaller planar dimension than the back layer and the surface layer, wherein;
the absorbent article including an outer peripheral region having the back layer and the surface layer bonded to each other without interposing the absorbent layer therebetween and being formed in a predetermined width spaced from a peripheral edge of the absorbent article; the back layer and the surface layer in the outer peripheral region are bonded to each other by bonding means adapted for being dissociated in water; and the bonding means is at least partially omitted to form an omitted portion.
In this aspect of the invention, the bonding means in the outer peripheral region of the absorbent article can enhance the shape retention of the article during its use, and when the absorbent article is, after used, disposed of in flush toilets, a large amount of water penetrates into the inside area of the article through the omitted portion of the bonding means, thereby facilitating the dissociation of the bonding means as triggered at the omitted portion. In addition, the water having penetrated into the inside area of the absorbent article through the omitted portion acts to remove air away from the absorbent article, and, as a result, the absorbent article thus containing water can readily sink in septic tanks and can be readily decomposed therein.
In particular, it is desirable that the omitted portion is provided at least one end edge in the longitudinal direction of the absorbent article.
No omitted portion is provided at both side edges in the transverse direction of the absorbent article. Therefore, while used, the absorbent article is free from the drawback of layer separation such that the surface layer and the back layer constituting it are peeled off from each other on both side edges in the transverse direction thereof owing to the movement of the body to which it is fitted.
For example, the bonding means is formed by heat-sealing the back layer and the surface layer with a thermoplastic water-soluble adhesive disposed therebetween.
The bonding means is partially omitted, and therefore immediately loses its bonding force when it receives a large amount of water, as triggered at the omitted portion. The absorbent article thus having lost its bonding force can sink in septic tanks and can be readily biodegraded. Therefore, the material for the bonding means in the absorbent article is not limited to only water-soluble adhesives such as PVA and others. As the case may be, the back layer and the surface layer constituting the absorbent article may be bonded to each other, for example, through mechanical compression sealing, or chemical hydrogen bonding, etc.
The absorbent article of the invention can retain its shape even when an adhesive is not provided between the surface layer and the absorbent layer and between the back layer and the absorbent layer in the inner region except for the outer peripheral region. However, so far as it does not detract from the decomposability of the absorbent article in water, the water-soluble adhesive may be provided between the surface layer and the absorbent layer and/or between the back layer and the absorbent layer to bond them in the inner region of the absorbent article.